One type of memory currently of interest utilizes magnetic tunneling junctions in the memory cells. A magnetic tunneling junction typically includes two ferromagnetic layers separated by a thin insulating layer. The insulating layer is thin enough to allow charge carriers to tunnel between the ferromagnetic layers. The resistance of the magnetic tunneling junction depends upon the orientation of the magnetizations of the ferromagnetic layers in the magnetic tunneling junction. If the magnetizations of the ferromagnetic layers are parallel, the magnetic tunneling junction is in a low resistance state. If the magnetizations of the ferromagnetic layers are antiparallel, then the magnetic tunneling junction is in a high resistance state.
FIG. 1 depicts a portion of a conventional magnetic random access memory 10. The conventional magnetic memory 10 includes a magnetic tunneling junction 12 and a resistor 14. The magnetic memory 10 also includes an operational amplifier 16, current sources 18 and 20 and voltage source 22. The state of the magnetic tunneling junction 12 is determined by comparing the resistance of the magnetic tunneling junction to that of the static resistor 14. In order to do so, the operational amplifier 16 is used to detect the difference in voltages developed across the magnetic tunneling junction 12 and the resistor 14. If the resistance of the magnetic tunneling junction 12 is greater than the resistance of the resistor 14, then the magnetic tunneling junction 12 is in a high resistance state. If the resistance of the magnetic tunneling junction 12 is less than the resistance of the resistor 14, then the magnetic tunneling junction 14 is in a low resistance state. Thus, the conventional magnetic memory 10 is a two state device.
Although the conventional magnetic memory 10 functions, one of ordinary skill in the art will readily recognize that it is generally desirable to increase the storage capacity of the a memory array.
Accordingly, what is needed is a system and method for providing a magnetic memory cell having an increased capacity. The present invention addresses such a need.